This invention relates to optically coupled semiconductive switching devices. The mounting of the light emissive diode on the semiconductive pnpn structure enables a good optical coupling efficiency which is further enhanced by the use of a high refractive index material to bond the components together so as to reduce reflection losses at the semiconductor/glass interfaces. A mesa construction of light emissive diode is used as it is found that the switching threshold of the pnpn triggerable structure appears to be more heavily dependent upon light flux density than upon total flux.